This invention relates to load cells, and more particularly to load cells having force sensing elements for measuring the applied forces.
One application of a load cell is to measure and monitor the strain forces (such as tension forces) on materials processed in the form of continuous webs or strands. Materials processed as webs include paper, plastic film, and metal foil; strands processed in this manner include wire, rope, and filaments. Measuring and controlling tension on the web or strand is an important factor in process quality, efficiency, and safety. For example, maintaining consistent tension promotes a more uniform web or strand product and avoids breakage and uneven stress in the product.
A typical load cell includes one or more force sensing elements, such as strain gages, which are configured as an electrical bridge circuit. The member deforms under the forces applied by the load (e.g., a roller of the aforementioned web or strand processing machine), thereby inducing changes in the resistance of one or more arms in the bridge and unbalancing the bridge. Electronic circuitry measures the extent of the imbalance, and determines therefrom the degree of deformation of the member. From this information, and from the load cell""s materials and design, the amount of strain induced in the memberxe2x80x94and hence the forces being applied by the loadxe2x80x94is determined.
This invention features a load cell that is capable of independently measuring differently directed components of forces applied by a load, and a method of measuring the force components with the load cell.
Among other advantages, the load cell is highly versatile can be used to measure loading forces applied in virtually any direction. Thus, the invention eliminates the need for load cells that are constructed differently to sense forces applied, e.g., in the vertical and horizontal directions. Moreover, there is no need to orient the load cell so that the force sensing elements are positioned with their direction of maximum sensitivity aligned with the direction of applied forces. Thus, the load cell is highly (but by no means exclusively) suited for use in web or strand processing machinery.
In one general aspect of the invention, the load cell comprising a member for receiving forces applied by the load, and a plurality of force sensing elements supported by the member and arranged with respect to each other to independently sense differently directed components of the forces.
Preferred embodiments may include one or more of the following features.
The force sensing elements are arranged to have substantially equal sensitivity to the differently directed components. The force sensing elements respectively sense orthogonally directed components of the forces. A first one of the force sensing elements is arranged to sense a component of the forces directed transversely to a plane of the member, and a second one of the force sensing elements is arranged to sense a component of the forces directed in the plane. The elements are supported by a portion of the member oriented in a first direction, and the second force sensing element is arranged to sense a component of the forces directed in the plane transversely (e.g., orthogonally) to the first direction.
Preferably, the force sensing elements are arranged in pairs, with a first force sensing element of each pair being arranged to sense a component of the forces applied in a first direction, and a second force sensing element of each pair being arranged to sense a component of the forces applied in a second, different direction. The force sensing elements are arranged so that the first force sensing element of each pair senses a component of the forces applied transverselyxe2x80x94and preferably orthogonallyxe2x80x94to a plane of the member, and the second element of each pair senses a component of the forces applied in the plane of the member.
Circuitry connected to the first force sensing element of each pair produces a first signal that indicates a magnitude of the component of the forces applied in the first direction. A second signal indicating a magnitude of the component of the forces applied in the second direction is produced by circuitry connected to the second element of each pair. In response to the first and second signals, circuitry produces an output signal that indicates a magnitude and direction of the forces applied by the load. The circuitry may also determine a force moment applied by the load.
The force sensing elements are preferably strain gages.
In another aspect of the invention, the load cell comprises a member disposed in a horizontal plane for receiving forces applied by a load, and a plurality of force sensing elements supported by the member, a first one of the force sensing elements being arranged to sense a component of the forces applied in a vertical direction relative to the plane, and a second one of the force sensing elements being arranged to sense a component of the forces applied in a horizontal direction relative to the plane.
Preferred embodiments may include one or more of the following features.
The plurality of elements includes a third force sensing element arranged to sense the component of the forces applied in the vertical direction, and a fourth force sensing element arranged to sense the component of the forces in the horizontal direction. Circuitry connected to the first element and the third element produces a first signal that indicates a magnitude of the component of the forces applied in the vertical direction, and circuitry connected to the second element and the fourth element produces a second signal that indicates a magnitude of the component of the forces applied in the horizontal direction. An output signal indicating a magnitude and direction of the forces applied by the load is produced by circuitry responsive to the first and second signals.
The member comprises a plurality of sections disposed in the horizontal plane for receiving the applied forces and an arm that interconnects the sections. The arm is oriented transversely to the component of the forces applied in the horizontal direction and supports the first and second force sensing elements; (e.g., strain gages). The member also includes a second arm interconnecting the sections. The second arm is oriented transversely to the component of the forces applied in the horizontal direction and supports the third and fourth force sensing elements (e.g., strain gages). The arms are disposed at opposite end regions of the sections. Preferably, the arms are parallel to each other, and the sections and the arms comprise a unitary body.
The load cell has a low profile and thus is particularly well-suited to installation under a so-called xe2x80x9cpillow blockxe2x80x9d which supports bearings at the ends of rollers in web (or strand) processing machinery. The low profile allows the load cell to be retrofitted beneath the pillow blocks of existing roller assemblies without drastically altering the locations (e.g., the heights) of the rollers.
Other features and advantages of the invention will become apparent from the following description, and from the claims.